<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>梯形</title>
    <style>
        /* 
            直角梯形
         */
        .trapezoid {
            height: 0;
            width: 100px;
            border-bottom: 100px solid red;
            border-right: 40px solid transparent;
        }

        /* 等腰梯形 */
        .trapezoid {
            height: 0;
            width: 100px;
            border-bottom: 100px solid red;
            border-right: 40px solid transparent;
            border-left: 40px solid transparent;
        }
    </style>
</head>

<body>
    <div class="trapezoid"></div>
</body>

</html>